1. Field of the Invention
This invention relates to a method of and a device for detecting the amount of ink in the ink fountain in a printer such as a stencil printer, and more particularly to such a method and a device in which the amount of ink is detected on the basis of the oscillation frequency.
2. Description of the Related Art
There has been known a printer such as a stencil printer in which ink is supplied to an ink fountain in a printing drum by an ink pump from an exchangeable ink container. In such a printer, the amount of ink in the ink fountain is detected by an ink sensor and when the ink in the ink fountain is consumed to a predetermined amount, the ink pump is operated to replenish the ink fountain with the ink from the ink container in order to keep constant the amount of ink in the ink fountain. (See, for instance, Japanese Unexamined Patent Publication No. 60(1985)-193687)
As a method of detecting the amount of ink, there has been proposed a method in which the tip of a needle antenna connected to an oscillator is dipped in the ink and the amount of the ink is detected on the basis of the oscillation frequency of the oscillator which varies with the depth to which the antenna is dipped in the ink. (See, for instance, Japanese Unexamined Patent Publication No. 58(1983)-62520) With this method, since as the depth to which the antenna is dipped in the ink increases, the electrostatic capacity around the antenna increases and the oscillation frequency of the oscillator lowers, the amount of ink in the ink fountain can be kept constant by replenishing the ink fountain with the ink so that the oscillation frequency detected becomes constant.
However, the oscillation frequency also depends upon the dielectric constant of the ink, and when the ink is small in dielectric constant, change of the oscillation frequency is small, which makes it difficult to detect change of the oscillation frequency with change of the amount of ink in the ink fountain. To the contrast, when the ink is large in dielectric constant, unnecessary radiation increases and the accuracy in detecting the change of the oscillation frequency is deteriorated. When detection of change of the oscillation frequency with change of the amount of ink in the ink fountain is difficult or the accuracy in detecting the change of the oscillation frequency is deteriorated, it becomes impossible to keep constant the amount of ink in the ink fountain and as a result, quality of the printed image deteriorates.
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and a device for detecting the amount of ink which can properly detect change of the oscillation frequency irrespective of the dielectric constant of the ink.
In accordance with a first aspect of the present invention, there is provided a method of detecting the amount of ink in an ink fountain in a printer on the basis of change of oscillation frequency wherein the improvement comprises
the step of changing the oscillation frequency on the basis of dielectric constant information on the dielectric constant of the ink.
The dielectric constant information may represent the dielectric constant of the ink itself, or may represent other factors such as the viscosity of the ink, the color of the ink, the time for which the ink is left to stand and the date of production of the ink on the basis of which the dielectric constant of the ink can be calculated.
The dielectric constant information may be obtained by measuring the dielectric constant of the ink or may be obtained from an information storage means attached to the ink bottle for supplying ink to the ink fountain.
As the information storage means, for instance, a nonvolatile memory (e.g., an EEPROM) which can hold data for a predetermined time interval without supplying power. This applicant has proposed a system for variously controlling a printer on the basis of information stored in such an information storage means attached to consumables like an ink bottle. See Japanese Unexamined Patent Publication No. 2001-18507.
Further the dielectric constant information may be input through an input means.
In accordance with a second aspect of the present invention, there is provided a device for detecting the amount of ink in an ink fountain in a printer on the basis of change of oscillation frequency wherein the improvement comprises
a frequency changing means which changes the oscillation frequency on the basis of dielectric constant information on the dielectric constant of the ink.
The frequency changing means may be arranged to obtain the dielectric constant information by measuring the dielectric constant of the ink and to change the oscillation frequency on the basis of the dielectric constant information thus obtained.
Further, the frequency changing means may be arranged to change the oscillation frequency on the basis of dielectric constant information provided from an information storage means attached to the ink bottle for supplying ink to the ink fountain.
The device may further comprises an input means so that the frequency changing means changes the oscillation frequency on the basis of the dielectric constant information input through the input means.
In accordance with the present invention, since the oscillation frequency is changed on the basis of the dielectric constant information, the change of the oscillation frequency can be easily detected by increasing the oscillation frequency when the ink is small in dielectric constant and, unnecessary radiation can be suppressed and the accuracy in detecting the change of the oscillation frequency can be improved by decreasing the oscillation frequency when the ink is large in dielectric constant, whereby change of the oscillation frequency can be accurately detected and the amount of ink in the ink fountain can be accurately detected irrespective of the dielectric constant of the ink, which makes it feasible to keep constant the amount of ink in the ink fountain and to obtain high quality images.